The long-term goal of this research is to understand the immune basis of acquired resistance to pre-erythrocytic stages of Plasmodium falciparum in humans. Studies done by ourselves and others suggest that T cell INF-y responses to selected vaccine candidate molecules mediate or are a surrogate of resistance against liver-stage P. faIciparum. Specific aims to determine the relevance of these responses to protection against hepatic-stage parasites are: 1. To characterize the repertoire of HLA class 1-restricted epitopes for the vaccine candidate molecules LSA-1 and TRAP in resident of a holoendemic area in the Wosera, Papua New Guinea. 2. To determine whether CD4, CD8, and CTL responses to TRAP and LSA-l epitopes are predictive of susceptibility to infection in partially resistance adults and increase with age in l to 3 year old children. 3. To evaluate the contribution of parasite allelic variation to heterogeneity of T cell responses in humans. Knowledge of these aspects of human immunity will facilitate development and evaluation of a human malaria vaccine.